cargo fix prepare-for 2018 errors after due to 'async' identifier

[seanmonstar]

I tried out cargo fix --prepare-for 2018 on hyper, and after it ran, it showed an error and claimed it was a bug in cargo or rustc, and to report it here. There is an identifier currently named async in a file, here: https://github.com/hyperium/hyper/blob/069a32b1acc5ece35643c26cf5d9972dace5481c/src/body/body.rs#L268

In this specific case, it would have been fine to just renamed that binding to async_, or perhaps r#async. I'm not sure if trying to do that automatically would accidentally name async blocks or functions wrongly, though.

[Nemo157]

Just hit this right now with websocket::async as well. It seems doing an unconditional replacement to r#async should work, the lint should only be triggered on identifiers so won't affect async fn, and async blocks don't exist in 2015.

EDIT: Except raw identifiers are still an unstable feature, should they be ungated in 2018 even though they're still unstable since they are essential for transitioning in some cases?

[alexcrichton]

Thanks for the report @seanmonstar and @Nemo157!

It looks like this may be a bug in the lint and/or compiler. To confirm, if you place #![feature(raw_identifiers)] at the top of the crate, does the migration succeed?

If so, I'll fix this in rustc. If not, there's more digging to do!

[Nemo157]

@alexcrichton #![feature(raw_identifiers)] worked, it updated the import to r#async and cargo fix didn't report any errors.

[alexcrichton]

Ok great, thanks for checking @Nemo157!

[alexcrichton]

Ok the fixes are now in nightly and with @Nemo157's confirmation it worked I'm gonna close, we can always reopen if this comes up again though!